This invention relates generally to gas turbine engines and more particularly, to prebooster and precompressor water injection in a gas turbine engine.
Gas turbine engines typically include a compressor for compressing a working fluid, such as air. The compressed air is injected into a combustor which heats the fluid causing it to expand, and the expanded fluid is forced through a turbine. The compressor typically includes a low pressure compressor and a high pressure compressor.
The output of known gas turbine engines may be limited by the temperature of the working fluid at the output of the high pressure compressor, sometimes referred to as temperature xe2x80x9cT3xe2x80x9d, and by the temperature of the working fluid in the combustor outlet, sometimes referred to as temperature xe2x80x9cT41xe2x80x9d. To reduce both the T3 and T41 temperatures, it is known to use an intercooler positioned in the fluid flow path between the low pressure compressor and the high pressure compressor. In steady state operation, the intercooler extracts heat from the air compressed in the low pressure compressor, which reduces both the temperature and volume of air entering the high pressure compressor. Such reduction in temperature reduces both the T3 and T41 temperatures. Increased power output therefore can be achieved by increasing flow through the compressor.
Typically, cool water or air circulates through the intercooler, and heat is transferred from the air flow to the cool water or air. The water or air absorbs the heat, and the heated water or air is then removed. Removing the heated water or air results in losses in total cycle thermal efficiency. Therefore, although an intercooler facilitates increased power output, the intercooler reduces thermal efficiency of the engine. The intercooler also introduces pressure losses associated with the removal of air, the actual cooling of that air, and ducting the cooled air to the compressor. Further, it is impractical for an intercooler to also provide interstage cooling.
With at least some known intercoolers, the heated water is removed using a water cooler which dissipates the heated water through a cooling tower as vapor into the environment. Of course, releasing the vapor into the environment raises environmental concerns. Also, a significant amount of water is required by such intercoolers, and such high water consumption increases the operational costs.
It would be desirable to provide a partial increased power output as achieved with intercoolers yet also provide improved thermal efficiency as compared to at least known intercoolers. It also would be desirable to provide increased power output even for single rotor gas turbines.
These and other objects may be attained by a gas turbine engine including prebooster or precompressor water injection which provides many of the same advantages, yet overcomes some shortcomings, of intercooling. In an exemplary embodiment, a gas turbine engine suitable for use in connection with water spray injection includes a low pressure compressor, a high pressure compressor, and a combustor. The engine also includes a high pressure turbine, a low pressure turbine, and/or a power turbine. A water injection apparatus is provided for injecting water into an inlet of the high pressure compressor. The water spray injection apparatus is in flow communication with a water supply, and during engine operation, water is delivered from such supply through the injection apparatus to the inlet of the compressor.
In operation, air flows through the low pressure compressor, and compressed air is supplied from the low pressure compressor to the high pressure compressor. In addition a water spray is supplied to the inlet of the high pressure compressor, and the water spray enters into the high pressure compressor through the inlet. Due to the high temperature environment at the location at which the water spray is injected, the water spray partially evaporates before entering the high pressure compressor. The water spray cools the air flow in the high pressure compressor for at least each stage of compression through which such spray flows, i.e., until it evaporates. Usually about by the mid-stages of the high pressure compressor, and depending on the water quantity, the majority of the water spray is evaporated.
The air and water vapor is further compressed by the high pressure compressor, and the highly compressed air is delivered to the combustor. Airflow from the combustor drives the high pressure turbine the low pressure turbine, and the power turbine. Waste heat is captured by boilers, and heat from the boilers in the form of steam may be delivered to upstream components.
The water spray provides an advantage in that the temperature of the airflow at the outlet of the high pressure compressor (temperature T3) and the temperature of the airflow at the outlet of the combustor (temperature T41) are reduced in steady state operations as compared to such temperatures without the spray. Specifically, the water spray extracts heat from the hot air flowing into and through the high pressure compressor, and by extracting such heat from the air flow, the T3 and T41 temperatures are reduced and compressive horsepower is reduced. The heat is removed as the water vaporizes. Reducing the T3 and T41 temperatures provides the advantage that the engine is not T3 and T41 constrained, and therefore, the engine may operate at higher output levels than is possible without such water spray. That is, with the above described water spray injection and using the same high pressure compressor discharge temperature control limit, the high pressure compressor can pump more air which results in a higher pressure ratio and a higher output.